Celestia's keen eyes scanned the bare room before her. Dark grey metal and concrete the same shade as a brooding ocean of storm-clouds. But whatever storm was brewing in this industrial wasteland of a room Celestia had no intention of getting caught up in it.

She had been bound in a manner most unbefitting of a princess: all four of her legs spread-eagled by the chains that were shackled to them. Her body was suspended by the fetters, dangling a few feet above the featureless floor. A further manacle had been attached to her horn, preventing her from turning her head to take in her surroundings. A peg on a rope dangled from the ceiling, attached to her tail, keeping the appendage lifted out of the way so that her marehood could be seen by whosoever might wish to view it.

She felt unbearably exposed with the chains pulling her legs wide open, like an insect pinned in some sick collectors display. The enormous spray-painted letters on the wall in front of her only exacerbated this feeling:

CELESTIA: SUBJECT 14

Somepony was going to get turned to stone or sent to the moon for this, of that Celestia was certain. It had been quite some time since anypony had been arrogant or foolish enough to think that mere chains could hold the Princess of the Sun.

Teleportation was the orthodox magic for escaping physical bondage but Celestia decided on using a heat spell to melt through the chains: a firm reminder of her power to drive the fear of God into her captors, whoever they were. She summoned up her magical might.

To no avail.

"Curses," she hissed to nopony in particular.

There were few things in the world that could neutralize her magical power for even a short period of time. She was immune to most of the poisons that were capable of such a feat and her aura resisted the magic neutralizing effects of a wide range of artefacts.

Nullstone. That must be it. This strange facility must be located on top of a nullstone ore vein. Celestia grinned.

Nullstone was a rare gem stone that emanated a particular wavelength that interfered with unicorn's and alicorn's ability to perform magic while in its presence. Nullstone was only found in the Frozen Northern part of Equestria and was notoriously heavy and difficult to mine meaning that the prison she was now held in would have to have been built on top of a vein of the stuff.

Excellent, she thought to herself, so this facility must be located in the North, not far from the Crystal Empire, I'd imagine.

Knowing where she was would only be step one of her escape plan. The other steps would be more... difficult without her magic.

"Princess Celestia?"

Maybe not as difficult as she had thought.

"Twilight!" she called to the familiar voice that had sounded behind her, "Is that you?"

"It is me!" replied Twilight, cheerfully.

Celestia breathed a sigh of relief. Her faithful student here to rescue her. Remarkable how quickly the young unicorn had managed to locate this strange facility but still, Twilight never failed to impress. She wished she could turn her head to look at the mare, who sounded like she was approaching from somewhere behind her, and she wished even harder that she could lower her tail to cover her most private area.

"Thank goodness you are here. Quickly, free me from these chains and then help me get to the bottom of whoever is responsible for this affront," as much as Celestia disliked giving Twilight orders, per se, the flush of embarrassment she was feeling at being exposed in front of her young student was disturbing her usual motherly demeanour.

"Sure... in a bit," said Twilight, sounding bizarrely noncommittal about the idea, "You know, Princess, I think I'm really making progress with my studies."

Seldom was Celestia left speechless but her student's sudden urge to talk about her studies while the Princess herself was dangling belly downwards from an array of leather ropes and steel chains was truly disturbing.

Celestia gasped as she felt the tickle of Twilight's breath on her nether region. It was almost as if the mare was talking to her lower mouth rather than to her, idly inspecting it as she spoke.

"The purpose of my early studies was merely the search for knowledge but as we moved into more complex lessons I came to realize that true wisdom was not merely having knowledge but knowing how and where to apply it in as ethical a manner as possible. Now I think I've finally moved on to the ultimate stage of my education," something sounded off about Twilight, her voice was strained and her breathing heavy.

Celestia tried and failed to look over her shoulder, the bindings still painfully restricting her head movement.

"Perhaps now is not the time to discuss such things, Twilight," Celestia tried but Miss Sparkle ignored her.

"The final stage of any scholar's journey should be to tackle the so called big questions. What is the meaning of life? Why are we here? What purpose does this all serve?" Twilight continued inspecting Celestia, pacing back and forth, observing her marehood from every angle.

"Twilight, I must insist that you help me get out of here this instant," demanded the Princess, rattling the chains that bound her as if to help remind the young mare of their current situation.

Twilight swept up next to Celestia, her mouth a hair's breadth from the Princess' cheek while still standing just outside of Celestia's peripheral vision.

"But I think I have an answer now. Would you like to hear it?" whispered Twilight.

Celestia gulped. Twilight Sparkle occasionally went a little crazy, as all ponies do every now and again, but she'd never heard the unicorn sound like this before.

"Reproduction," hissed the purple unicorn into her mentor's ear, "Intercourse. Mating. Breeding. Rutting. Sex. Copulation... fucking."

Celestia bit her lip and wriggled against the chains as she felt her student's tongue dip into her ear momentarily after each and every word. The blush that had been playing on the Princess' cheeks deepened to a darker, richer hue.

"Twilight! Have some shame, for goodness sake! What has gotten into you?" fear, an unfamiliar concept for an immortal sun princess, was beginning to rise in Celestia's chest.

"The purpose of life is to create life! To pass on one's own genetic material. To survive one's own demise through the creation of offspring. As many as possible. The purpose of life is to attain pleasure and sex is pleasure itself. Don't you understand? It's not hedonism if it serves a purpose and the purpose is to commence the cycle anew," Twilight finally walked around to face the Princess head on.

What made Celestia draw a sharp breath was not Twilight's ruffled mane or the rather wild look in her eyes but the enormous cock dangling from her loins. Greasy, slick, veined and purple, the thing was rock hard and rearing to go, straining against its own skin. Two swollen grapefruit sized testicles hung between her beloved student's leg, forcing the unicorn to walk bow legged.

"Twilight... what have they done to you?" said Celestia, her voice trembling with horror.

"They merely gave us the tools. We did it to ourselves. We chose. Just like you will choose. I watched the others. They made me watch as each of them fell. This is what we were made for after all. Some will take the role of males, others of females and others of both. But ultimately all must submit to their true purpose. We exist to breed, Celestia. It's what we do best. You'll understand soon," Twilight licked her lips to prevent a strand of drool from running down her chin. The mare's lust was beyond the point where it could be controlled.

"You're wrong, Twilight. And if you'll just let me out of these chains then I will show you the way back to normality. I promise you. I can fix this if you'll let me. You know you can trust me," Celestia's voice was shaking but she managed a weak smile to comfort the broken pony. It accomplished little.

"You think I'm not normal right now and I think I should be the new norm for all ponies. Clearly we've reached an impasse. But science isn't about trust. If we want to discover which of us is truly correct we will need to experiment," Twilight gave her mentor a manic grin and trotted back around to the other side of her.

"I told them that you would be unable to bear foals. Because you have been alive so long your cells have been put into a kind of magical stasis to avoid aging at all. Your womb is completely inert, you don't have periods, you don't ovulate and you cannot reproduce. But this is fairly easily rectified. The cellular hibernation is held in check by the stability of your psyche. So if I were to... say for example..." Twilight gave Celestia's marehood a tentative sniff, "Alter your mind in some way... permanently change your priorities... break you like they broke me... I think your cells would return to normal. You'd be mortal once more but in addition you'd be capable of reproducing which is, in case you forgot, the purpose of life."

"No! Twilight, come back. Come back round to the front and talk to me. Twilight! Twilight, please," Celestia tugged desperately at her chains, hoping against hope that she could at least get a single hoof free to protect herself.

"But since I am an academic sort of pony I always keep an open mind to other's points of view," chuckled Twilight as she placed her forehooves on Celestia's voluptuous arse cheeks, "So here's how this will work. If you can endure one hundred thrusts then I will be forced to conclude that I was indeed mistaken about the true meaning of life and then I'll free you from here and we can all go home together. If you break before then well... let's just say that my hypothesis will be confirmed. Don't worry about lubrication, by the way. Rarity's juicy snatch got me nice and slick just before you arrived."

Celestia's voice caught in her throat as she felt the head of Twilight's scrape past her clit as it trailed its way up to position itself in front of her opening.

"Let the experiment begin," Twilight said, swinging her hips back to give her cock a running start for the first thrust.

She slammed into Celestia like a runaway freight train, forcing nearly all of her length deep inside the Princess as both mare's moans broke the silence. The room was filled with puffs and whimpers as Celestia adjusted to having her hole stretched wide by Twilight's impressive girth and Twilight accustomed herself to her mentor's tightness.

"Twilight's log, day four: first use of Celestia's hole," mumbled Twilight in between shivers of pleasure, "S-s-subject is remarkably warm on the inside and s-s-surpisingly tight for such an old pony. I was not expecting that and should p-p-probably not have thrust in so hard if I'm going to pace myself for a full hundred thrusts. Now attempting thrust number two."

Twilight heaved her hips back. Celestia's royal pussy clung hungrily to her purple shaft as if it never wanted to let go. The two of them let out throaty groans as each inch of the shaft was hauled out of Celestia's vicelike grip. Twilight returned herself to her starting position, the tip still just barely inside. Suddenly and without warning she wrapped her forelimbs around the much larger mare's midriff and plunged back inside. Not quite balls deep but deeper than before.

Celestia bit her lip and squeezed her eyes shut tight as her cunt clenched and unclenched on the enormous intruder.

"Second thrust successful," gasped Twilight, burying her face in Celestia's flowing mane, "Tightness is v-v-very impressive. She's actually quite muscular. Alicorn's get the strength of earth ponies along with the wings and horn, I suppose. Now that I think of it Celestia's transcendent state probably means she's usually above lust. I may be the first pony to be using this hole in over a thousand years. Would that be accurate?"

Celestia couldn't answer. It had been an awfully long time since she had last had a lover and she certainly didn't remember sex being even half this intense.

"M-m-my only complaint is that it's a little dry. The friction is quite fierce on entry. Still, we'll see how it goes..." Twilight pulled back her hips for another thrust.

"No wait... Twilight, at least give me a second to recover so-" Celestia was cut off as Twilight re-entered. The Princess' cunt loosed a shower of steaming hot fluids that gushed down the sex-crazed unicorn's shaft and dripped off the bloated, hairless testicles. As the warm clear liquid splattered on the floor Twilight basked in the ever growing warmth of the Sun Princess.

"Dryness problem solved itself," she whispered, lost in a dreamlike state, "The heat of this thing is incredible. Way above normal body temperature. She achieved orgasm on only the third thrust. I suspect I was right in my belief that she has not been f-f-fucked in a long while. You n-n-never told me you were a squirter, Princess. But then again I guess I never asked. Ninety seven thrusts to go. Get ready. This time I'm going to put the whole shaft inside."

Celestia could only whine like an animal caught in a trap as she continued dripping long pent up juices. Her entire body trembled as Twilight's flare scraped along her inner wall on its exit journey.

Twilight reached forward and grabbed her mentor's mane like reins. With the chain attached to Celestia's horn pulling one way and Twilight's hooves yanking her hair the other the Princess could only dangle and wait as Twilight prepared the next thrust.

And swiftly it came. This time the entirety of the shaft forced its way in, slamming into the opening of the Princess' womb and hammering through it like a battering ram. Twilight hilted herself inside her teacher but continued to push forward as if she had more shaft still to squeeze inside.

"Excellent texture. Velvety but firm. This one is my favourite, I think, out of all the others. I'll use it again and again once I've broken it in. She'll make a fine broodmare," Twilight was now looking down on the pony she had admired most as a mere sex object. Soon to be another addition to the list of the mare's she'd emptied her swollen balls inside. This was how she had come to treat all the others. As experiments in pleasure. Toys to aid her in her ascension.

Lost somewhere in the hurricane of pleasure Celestia was both aroused and revolted by the thought of her dear student being corrupted in this way. But such complex thoughts vanished from her mind as the head of Twilight's member kissed the innermost part of her womb.

Twilight released her mentor's mane and settled on gripping both of the Princess' now splayed and twitching wings.

"Your womb is reacting to this, Celestia. It shouldn't be throbbing like this if its truly in stasis like the rest of you. Be careful. If you let your psyche get lost in the pleasure then I really will be able to impregnate you. They used drugs to raise my sperm count through the roof. I've already impregnated Rarity, Applejack, Fluttershy and I would have gotten Rainbow if Pinkie hadn't gotten her first. So I impregnated Pinkie as well. And you're going to be next..."

Twilight didn't bother drawing her hips all the way back for the fifth thrust. She simply pulled back enough for the head of her cock to pop out of the mouth of Celestia's womb before she burst back inside it.

Celestia's back arched as far as the chains would allow and she loosed another drenching flood of boiling hot marecum onto the floor. Her tongue waggled in the air like a dying insect, her jaw slack and eyes squinted and watering.

"You came again?" giggled Twilight, "We're only on the fifth thrust, Celestia. Ninety five still to go before I let you go... if I let you go. I thought you wanted to help me go back to being normal? I thought you wanted to save me from this? Can't you endure a mere hundred thrusts to bring your beloved student back from this terrible place? We've only done five thrusts and you're squirting like a whore- ah!"

Celestia's royal princesshood suddenly constricted, pinching down on Twilight's shaft. Twilight simply laughed.

"Subject seems to enjoy being abused verbally. Don't you... slut?"

Twilight sneered as the Princess tightened down once more, plot hole winking at her student with each clench.

"Commencing earnest copulation," said Twilight as she began pounding steadily at Celestia's marehood. Her cock sliding in and out with a steady but firm pace.

Celestia's lips scrunched up as her pussy was stuffed. There was an unbearable warmth building up inside her foal factory. Twilight was right. It was preparing itself. The tubes were waking up as if from a long sleep, readying her for insemination. She knew that she needed to compose herself, formulate a plan of escape, return to her usual placid frame of mind. But each time Twilight slammed back inside her psyche rippled like a pond that was being bombarded with pebbles. Another orgasm coursed through her veins and she howled like an animal.

"Third orgasm after eleven thrusts. Seems like she doesn't have much left to squirt. Subject is... breaking nicely. Increasing... ah... speed... at this... time..." True to her word Twilight picked up the pace.

A wet, meaty slapping noise filled the air as Twilight swung her hips back and forth, shoving her enormous purple cock inside her new toy. Celestia continued to leak her unnaturally hot excretions onto the concrete below her. The Princess' eyes began to roll back in her head, her tongue dangling helplessly out of her mouth, panting like a dog. Her consciousness felt like it was somewhere far away, tethered to her body by the unbelievable pleasure that being used by her student was bringing her.

She had almost raised this mare herself. She'd read her bed time stories when she was just a filly. She'd sung lullabies for her. She'd held her hoof when she was frightened and taught her everything she could. And now she was being mercilessly ridden by that same mare. Relentlessly broken. Twilight's movements were growing frantic. A feverish pitch of primal and loveless rutting.

"Fifty one, fifty two... ah... fifty three, fifty four, fifty five... feeling good down there? Enjoying yourself? I told you... ah... fifty nine, sixty...this is why we exist... sixty two, sixty three... your womb is suckling at me... sixty six, sixty seven...you know I'm right, you filthy alicorn cumdumpster... ah... seventy, seventy one... you want this... seventy four... you want this, don't you bitch? Twilight's log... ah... subject is lost in a... ah... state of constant orgasm... seventy nine, eighty..."

Twilight was making full use of her discovery about how Celestia's marehood reacted to abuse. She might have hypothesized that it was because the Princess was treated so politely by everypony that she must have developed a kind of masochistic yearning. She might have hypothesized as much had she not been devoting her entire being to fucking the daylights out of her new broodmare. She gave the broad backside a solid slap with her hoof right on the sun shaped cutie mark, relishing the feeling of the cunt she was in the process of dominating.

"I'm getting close... eighty eight, eighty nine... so close... can't take much more... ah...ninety four, ninety five... just a little more... gotta hold it in... ninety nine and... ah... one hundred," Twilight pulled her cock out after the hundredth thrust with a wet, popping sound. She was on the absolute brink, leaking dollops of precum which mixed their milky whiteness with the clear viscous slime that Celestia's marehood had coated her cock with.

"There we go, Celestia... you made it! Now we can go home. I'll unlock your shackles now, shall I?" said Twilight, breathlessly. Halting herself on the brink of cumming had taken a degree self control that Twilight had not had in the first few days in the Milking Chamber.

Celestia was awoken from her daze by the sudden aching sensation of emptiness. She desperately writhed, rocking back and forth in the array of chains that held her suspended in the air.

"N-n-no..." she whispered, her womb in full bloom: returned from its long stasis and now in all its carnal glory. Fresh and fertile.

"No, what?" taunted Twilight, playing innocent.

"Don't... s-s-stop..." stuttered Celestia, still having difficulty processing words after her lengthy ordeal.

"But Celestia... I thought you were going to save me... if we keep going then I'll cum inside your womb... and you'll be sure to get pregnant... and even if you don't get pregnant then Pinkie, AJ, Rarity and myself will continue to pump your womb full of spunk every second of every day until we can be sure that you do. You'll never leave this place again. We'll keep you in a cage and feed you nothing but semen. We'll fuck you so hard you'll forget who you were. And you'll never save your precious student. Is that what you want?" Twilight touched the tip of her cock to Celestia's now red and puffy marehood.

Celestia swallowed. She couldn't fight it. Couldn't stop herself. She struggled to find the words.

"Beg," Twilight said simply, "Beg for it."

"Puh-p-p-please... please give y-y-your p-p-princess..."

"You're not a princess anymore," said Twilight sternly, "What are you?"

"C-c-cum dumpster broodmare," whined Celestia, the tip of Twilight's cock dipping a delirium inducing few inches into her and then pulling away again, "P-p-please impregnate m-m-me... use me as your own... p-p-private s-s-slut. F-f-fill me up again and again... please-"

Twilight interruped her before she'd finished. Hurtling back into her, puncturing her womb and emptying a squirt of impossibly thick horse cum into the former Princess.

"Subject successfully broken. C-c-commencing insemination!" Twilight bit her own lip and unleashed a bucket load of cum directly into Celestia's baby sack. The larger mare could handle a bigger load than most but Twilight's enormous scrotum seemed capable of releasing an impossible quantity. The alicorn's womb ballooned up as it was pumped full, the tip of Twilight's dick forming a cork to ensure none of it escaped.

They both knew on some deep instinctual level that Celestia had been impregnated without even a shred of doubt. The entirety of her womb was filled to the brim, even her tubes were flooded. Squirt after glorious squirt was fed into her, her belly beginning to swell as if she were well on the way to birthing Twilight's foal already. Twilight struggled to keep her cock inside, the pressure that the semen had built up was almost forcing her out. She smiled.

"Pinkie Pie! Applejack! I know you two are in the observation bay watching this! Come down here right now!" she pulled free of her former mentor's cunt, letting loose the marble river that she had been holding inside and giggling as it rushed out and splattered onto the floor.

She turned as a steel plate on the wall behind her slide open.

"You girls can have a turn with her for a bit."

Author's Notes:

I know what you're thinking. Why didn't you do a chapter that got more thumbs up... well... thats cos I forgot to check the second page of comments before I wrote. I'll probably do one of the musicmans idea next... I'm thinking DT and Apple Bloom... unless the votes shift elsewhere. Keep voting, I'm sure I'll do all the most popular requests before I run out of steam